An ultramicro adaptation of the glucose oxidase method requiring only five microliters of blood was developed to study glucose tolerance of C57BL/Ks mice from one week of age through full maturity. Serum IRI levels were also determined ½ hour following intraperitoneal administration of glucose (2 mg./gm. body weight) and L-leucine (0.2 mg./gm. body weight). Glucose tolerance tests were performed by obtaining tail blood from fed mice immediately prior to (0 time) and 1/2, 1, 2 and 3 hours following intraperitoneal injection of 2 mg. glucose/gm. body weight. Results indicated that mean baseline (0 time) blood glucose levels were lowest in one-week-old mice (92 mg./100 ml. blood) and reached levels observed in adult animals by five weeks of age (142 mg./100 ml. blood). Despite the low baseline blood glucose at one week of age, these same animals exhibited marked and sustained hyperglycemia following glucose administration with mean levels of 469 mg./100 ml. blood and 401 mg./100 ml. blood at 1/2 and 3 hours, respectively. By two weeks of age glucose tolerance was improved ½ hour = 306 mg./100 ml. blood, 3 hours = 97 mg./100 ml. blood). By three weeks of age glucose tolerance curves appeared similar to those in adult animals. A significant difference between glucose tolerance in male and female mice was noted as early as eleven weeks of age. The marked glucose tolerance in one-week-old mice was explained, at least in part, by failure of these animals to show a significant rise in circulating serum IRI levels following glucose administration despite having the capability to secrete insulin in response to parenteral L-leucine.

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